Graft reaction via melt processing equipment such as single or multiple screw extruders, rubber masticators, Banbury processors, Brabender processors, roll-mills and the like, includes well-known technology and is widely reported in the technical literature. Similarly, post-graft reactions with the graft polymers are also widely reported. Thus, the graft reaction of unsaturated carboxylic acid or carboxylic acid derivatives with thermoplastic polymers capable of subsequent chemical reaction for use in such as lubricating oil compositions or thermoplastic blend compositions has become an important field of ongoing development. The following patent art addresses such graft reactions, particularly one suitable for the preparation of lubricating oil additives.
U.S. Pat. No. 3,862,265 addresses degradation in molecular weight to achieve narrow molecular weight distribution, and optional free-radical initiated graft reaction of unsaturated monomers with, for example, ethylene-propylene copolymer by use of melt processing procedures in an extruder reactor. Intensive mixing of free radical initiator and graft reactants with molten polymers is achieved by the use of either decompression zones or thin film zones in the extruder. An additional suggestion for product quality improvement is that of capping the reaction zone to prevent escape of gaseous reactants, and accompanying that with subsequent venting under reduced pressure to remove vaporous components. The suggestion is further given that subsequent reaction in the extruder can modify the graft-monomer-containing polymers, specifically such subsequent reactions as those of esterification, neutralization, amidization and imidization.
U.S. Pat. No. 4,320,019 describes the preparation of lubricating oil additives that are reaction products of interpolymers, of ethylene, C.sub.3 -C.sub.8 alpha olefins, and polyenes that are first reacted in an oil solution with olefinic carboxylic acid compositions, and then with an amine. The reaction of the interpolymer with the acid compositions are conducted at temperatures and conditions designed to avoid molecular weight degradation. It is said that unreacted materials can be removed by vacuum stripping from the oil solution. The reaction with amine is generally taught to be conducted in solvent in subsequent steps.
U.S. Pat. No. 4,670,173 describes the preparation, under either solvent-free or solution based conditions, of lubricating oil additive compositions that are the reaction product of an (D) acylating reaction product, a (F) polyamine and a (G) mono-functional acid. The (D) acylating reaction product is prepared by reacting a (A) hydrogenated block copolymer and (B) alpha-beta olefinically unsaturated carboxylic reagent in the presence of (C) free radical initiators. The solvent-free reaction can be conducted in an extruder with high mechanical energy to achieve necessary chain scission, though such is said not to be usually desired. The (D) acylating reaction product is dissolved in solution, separated and dried, desirably with removal of unreacted (B) carboxylic agent such as vacuum stripping. A subsequent solvent-free reaction with a primary amine compound in an extruder is described, see Example 10 of U.S. Pat. No. 4,670,173.
U.S. Pat. No. 4,749,505 similarly addresses the preparation of lubricating oil additive compositions by melt processing reaction and simultaneous degradation of ethylene copolymers containing C.sub.3 -C.sub.8 alpha olefins, and optionally, non-conjugated diolefins. The melt processing reaction is conducted under nitrogen in the presence of a free radical initiator with an optional simultaneous grafting of ethylenically unsaturated carboxylic acids or nitrogen containing monomers. If carboxylic acid is grafted, a subsequent reaction with an amine or hydroxy component is said to be possible with undiluted graft copolymer, in a separate reaction vessel. Nitrogen purging of the initially formed carboxylic acid grafted copolymer prior to the addition of oil diluent for subsequent reaction with a primary amine is described in Example 2.
European Patent Application publication 0 422 728 A1 describes an extruder process for preparing a dispersant viscosity index improver aminated polymer comprising the steps of (a) free radical grafting of an alpha-beta unsaturated carboxylic acid moiety onto either of (i) selectively hydrogenated block copolymers of conjugated diene and monoalkenyl arenes or (ii) hydrogenated polymers of conjugated diolefins, and (b) reacting the functionalized polymer with an amine. The graft functionalization of step (a) is done under conditions of high energy mixing in the presence of 3.0% to 15% by weight of polymer of diluent oil. Additionally, the free-radical initiator is added after the carboxylic moiety to avoid cross-linking and coupling. Removal of a portion of unreacted carboxylic acid reagent, 20-80%, and as well reaction by-products and unreacted amine, is described by vacuum assisted venting after the graft reaction zone in which the amine is reacted with the acid grafted polymer.
As demonstrated in the technical literature discussed above, it is of continuing importance to provide functionalized thermoplastic copolymers and to provide cost-effective means of preparing them while minimizing or eliminating undesirable by-products that can adversely affect subsequent reactions and utility in end-use applications. In particular, it is important in the preparation of lubricating oil additives to eliminate unreacted carboxylic acid reagent, free-radical initiator decomposition products, low molecular weight oligomers, by-products created when unreacted amine reacts with non-grafted carboxylic acid. Further, the artionic polymerization of unsaturated carboxylic acid moleties in the presence of certain highly polar reactants, e.g., Polyamines that are desirable otherwise in many applications, not only competes with desired reactions but can create polymeric by-products that are not easily removed by vacuum venting alone at the temperatures and pressure optimal for the thermoplastic melt processing.
It is thus a principle object of this invention to provide an efficient and cost-effective means of preparing functionalized thermoplastic polymers in neat form requiring none to minimal purification subsequent to preparation by the present process. Another object of the invention is the economic preparation of certain graft polymers that are useful in lubricating oil compositions as multifunctional viscosity modifiers and other graft polymers that are useful as modifiers for engineering thermoplastics. Additional objectives will occur readily to those skilled in the art from the following specification which describes the invention in detail.